05000388/LER-2017-001
| Event date: | 06-1-2017 |
|---|---|
| Report date: | 05-65-2017 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 3882017001R00 - NRC Website | |
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
2017 - 00
CONDITIONS PRIOR TO EVENT
Unit 1 — Mode 1, approximately 100 percent Rated Thermal Power Unit 2 — Mode 5, approximately 0 percent Rated Thermal Power There were no structures, systems, or components that were inoperable at the start of the event that contributed to the event.
EVENT DESCRIPTION
On March 6, 2017 at approximately 1325 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.041625e-4 months <br />, both airlock doors [EIIS Component Identifier: DR] of a secondary containment airlock [EIIS System/Component Identifier: NG/AL] were momentarily open at the same time causing an alarm [EIIS Component Identifier: ALM]. The following provides details of the event:
The event occurred at the Unit 2 airlock between the turbine building (TB) [EIIS System Identifier: NM] and reactor building (RB) [EIIS System Identifier: NG] on Elevation 676. Individuals on the TB side of the airlock verified a green light and opened the TB side door, causing the RB side door to pop open from differential pressure. The individual on the RB side, who was using the security card reader, saw the RB door pop open. The doors were immediately closed, reestablishing secondary containment.
Investigation identified that the latch on the RB side door appeared to be sticking (e.g. not fully returning to the latched position once released) when the crash bar was engaged.
With both airlock doors open simultaneously, Surveillance Requirement (SR) 3.6.4.1.3 was not met. The condition is being reported in accordance with 10 CFR 50.73(a)(2)(v)(C) as a condition that could have prevented fulfillment of a safety function.
CAUSE OF EVENT
The cause was determined to be sticking of the RB side door latch inside the crash bar, which prevented the door from properly latching and staying latched when differential pressure was applied, such as when the TB side door was opened. The most likely cause of the crash bar latch failing to reset properly is abnormal wear from heavy use during outage mobilization exacerbated by mechanical damage suffered during impacts with wheeled carts carrying material through the airlock.
ANALYSIS/SAFETY SIGNIFICANCE
An engineering evaluation was performed and concluded that secondary containment could have performed its safety function of isolating as assumed in the accident analysis and also of re-establishing 0.25 inches vacuum (drawdown) within the assumed accident analysis time (10 minutes). Therefore, the subject event did not cause a loss of safety function. This event will not be counted as a safety system functional failure (SSFF) for the NRC performance indicator based on the engineering analysis that shows there was no loss of ability to fulfill the safety function.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
CORRECTIVE ACTIONS
Key corrective actions include the following:
1. The crash bar on the RB side door was replaced.
COMPONENT FAILURE INFORMATION
Reactor Building Elevation 676 Door 120A Latch
PREVIOUS SIMILAR EVENTS
The following are recent LERs involving loss of secondary containment due to human performance issues associated with airlock doors:
dated April 12, 2017.
dated March 8, 2017.
dated January 26, 2017.
Error," dated November 21, 2016 dated December 1, 2016 Error," dated August 17, 2016 A Human Performance Error," dated June 15, 2016 A Human Performance Error," dated June 9, 2016 Double Airlock Doors," dated June 9, 2016 Due to Degraded Latch Mechanism," dated May 26, 2016.
Due to Degraded Latch Mechanism," dated May 24, 2016.
Human Performance Error," dated May 16, 2016.
Inoperable Due to Airlock Doors Open Due to